Contrary to `CompositorNodeCustomGroup` or `ShaderNodeCustomGroup`, `GeometryNodeCustomGroups` have to define their own poll function. This is because their is no predefined poll function for `GeometryNode`, and it may not be clear for addon developers why `GeometryNode` would be special here. This adds `GeometryNode` to `bpy_types.py` and defines such a function for it like for other builtin node types. Differential Revision: https://developer.blender.org/D14775